1. Field of the Invention
The present invention relates to a color cathode ray tube, and in particular o a color cathode ray tube which is capable of obtaining a high picture quality by minimizing the distortion of a picture by designing an internal curvature of a panel to an optimum shape.
2. Description of the Prior Art
In general, as depicted in FIG. 1, a color cathode ray tube includes a panel 3 coated on a rear surface with a R, G, B fluorescent screen 1, an funnel 4 coupled to a rear edge of the panel 3, an electron gun 7 inserted into a neck portion 5 of the funnel 4 and emitting an electron beam 6, and a shadow mask 8 installed at the rear of the panel 3 with a certain distance and having a plurality of holes as passages for the electron beam 6. The shadow mask is typically under a tension.
In the prior art, as depicted in FIG. 2, in an internal curvature of the panel 3, a radius Rd of a diagonal curvature is larger than a radius Rv of a short side curvature and is smaller than a radius Rh of a long side curvature.
In more detail, in the panel 3 in accordance with the prior art, Rh/Rd is not less than 1.1, and Rv/Rd is not greater than 0.8.
When the radius difference between the long side curvature, short side curvature and diagonal curvature is large, because a structural stiffness at a corner portion of the shadow mask 8 is reduced especially, the shadow mask 8 may be easily deformed due to an outward impact, and accordingly a drop characteristic drastically decreases and an image distortion occurs.
In addition, when an electron beam is emitted in a horizontal direction or a vertical direction in a general cathode ray tube, the distance from a deflection center to a center portion, a short side portion or a long side portion of an screen effective surface area is different from each other, and accordingly when a vertical line or a horizontal line is displayed, an image distortion phenomenon occurs (i.e., the vertical line or the horizontal line is distorted). The image distortion phenomenon becomes more serious in a scaled-up and flat screen cathode ray tube.
In particular, when an operation such as a CAD (Computer Aided Design) is performed, a straight line may be distorted as a curved line or a true circle may be distorted as an oval shape, and accordingly the usefulness is drastically reduced.
In order to solve the above-mentioned problems, it is an object of the present invention to provide a color cathode ray tube which is capable of increasing the structural stiffness of a shadow mask and improving a reliability about an outward impact by designing a radius of long side curvature, short side curvature and diagonal curvature as an optimum state.
In order to achieve the above-mentioned object, there is provided a color cathode ray tube having an almost flat screen outer surface and an internal panel curvature satisfying the following conditions:
0.98 less than Rh/Rd less than 1.02,
0.95 less than Rv/Rd less than 1.04,
0.98 less than Rt/Rh less than 1.02, and
0.98 less than Rs/Rv less than 1.05,
wherein Rd is the radius of diagonal section curvature within a screen effective surface area, Rt is the radius of circumference section curvature along a long side, Rs is the radius of circumference section curvature along a short side, Rh is the radius of section curvature on the x axis passing through a center of the screen effective surface area and parallel to the long side, and Rv is the radius of section curvature on the y axis passing through the center of the screen effective surface area and parallel to the short side.